Flour percentages and flavor impact

Had a question today on flours. Went out over the weekend and procured some different varieties, then whipped up a couple of loaves. The following are the recipes I used:

500g Poolish starter (1:1:1 ratio)

275g water

400g RM White

50G KAF WW

30G RM Oat

20G RM Spelt

20G salt

Version 2 I subbed Rye for the Oat.

S&F method, fold and rest thrice, 10 minute rests. BF 3hrs (warm day). 2 Folds at 10 minutes, 2 Hr FP. In at 450 for 40 minutes with steam and this is what I got:

On the right is the Rye variety. I found these both to be quite similar, though the addition of the Spelt seems to have impacted them nicely. Nuttier ( a bit, more balanced, crumb is good).

However, the difference between the two was hard to discern. I set a 4% mark for the spelt and 6% for the Oat/Rye. Question: Anyone have a good "experimental" percentage that seems to give us some cornerstone for getting some real flavor changes? I'm gonna bump to 10% next time.. see what happens. Appreciate thoughts/comments.